Magnetic recording medium

ABSTRACT

A magnetic recording medium includes a metal magnetic layer (4) formed on a nonmagnetic base (1). On one major surface (1A) of the nonmagnetic base (1) is formed a metal layer (2) at least the surface of which is oxidized, nitrogenated or carbonized on which the metal magnetic layer (4) is further formed. This magnetic recording medium is capable of improving the durability of the metal magnetic layer (4).

DESCRIPTION

1. Technical Field

This invention relates to a magnetic recording medium and particularlyto a so-called thin film magnetic recording medium having a metalmagnetic layer formed on a nonmagnetic base and especially to improvethe durability such as adhesion to the nonmagnetic base, wear-proofproperty and so on the metal magnetic layer.

2. Background Art

While it was previously proposed in this kind of a thin film magneticrecording medium tha a continuous film made of a metal such as Al, Tiand so on or organic substance should be interposed between anonmagnetic base and a metal magnetic layer for the purpose ofincreasing the adhesion of the metal magnetic layer to the nonmagneticbase, this was far from satisfactory.

DISCLOSURE OF INVENTION

According to the invention, a metal layer at least the surface of whichis oxidized, nitrogenated or carbonized is formed on one major surfaceof a nonmagnetic base on which a metal magnetic layer is further formed.According to this invention, the durability of the metal magnetic layerof the magnetic recording medium can be improved (from several times toten-odds times as that of the prior art), resulting in a magneticrecording medium of high reliability.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 through 5 are cross-sectional diagrams each showing an exampleof a magnetic recording medium of this invention in the order of itsmanufacturing process.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the drawings, a magnetic recording medium according to thisinvention will hereinafter be described in detail in conjunction with amanufacturing process thereof.

In the present invention, first, as shown in FIG. 1, there is prepared anonmagnetic base, for example, a polyethylene telephthalate-base 1, andthen one major surface 1A of the base 1 is subjected to activationtreatment. This activation treatment is performed by disposing thenonmagnetic base in plasma of an atmosphere gas generated by coronadischarge in an atmosphere containing low pressure oxygen, for example,vacuum degree of the atmosphere is from 10⁻¹ to 10 torr. As an exampleof the atmosphere, there can be utilized atmosphere of a mixed gas of70% of Ar with 30% of O₂ in which the pressure of O₂ gas is 10⁻³ torr(hereinafter, this atmosphere is called atmosphere a). But, theatmosphere gas for this activation treatment to be activated is notlimited to gas containing oxygen, but any gas, for example, even argongas alone makes the activation treatment possible.

Next, as shown in FIG. 2, on the activated major surface 1A of the base1 is formed by a process such as vacuum deposition, sputtering or thelike a discontinuous film, namely, island-shaped portions 2 made ofmetal or cobalt Co which the example of this invention utilizes. Theisland-shaped portions 2 have a mean film thickness of about 10 to 1000Å or about 300 Å the example of this invention utilizes. For the metalwhich is utilized for the island-shaped portion 2, there can be employedAl, Ti and so on other than Co. Nonetheless, Co is most preferable, thereason of which is that since Co is the same as the component of a metalmagnetic layer which will be formed later, only one evaporating sourceis enough, giving rise to improvement of productivity. As a manner ofthe vacuum deposition, while either of vertical and oblique evaporationscan be utilized, the oblique evaporation rather allows the discontinuousisland-shaped portions to rather easily be formed.

Next, as shown in FIG. 3, the oxidizing atmosphere (gas containing morethan 20% of O₂ gas (the remaining gas is inert gas)), nitrogenatingatmosphere (gas containing N₂) or carbonizing atmosphere (acetylene gas,ethylene gas and so on), is formed and applied with a DC voltage to thisatmosphere gas to generate plasma of the atmosphere gas. Then, exposingthe base film on which the metal layer was formed as the island-shape tothis plasma, the surface of the island-shaped portions 2 or the overallinside thereof is formed as oxide, nitride or carbide 3. For thecondition of plasma, atmosphere gas of gas pressure ranging from 10⁻¹ to10⁻⁴ torr is introduced and the voltage to be applied is selected in therange from several hundred volts to several thousand volts. In theexample of this invention, the surface of the island-shaped portions istreated in the plasma which was generated in the aforesaid atmosphere acontaining oxygen to form the oxide 3 of cobalt on the surface of theisland-shaped portions 2 made of cobalt.

In the process of FIG. 2, under the oxidizing atmosphere, nitrogenatingatmosphere or the carbonizing atmosphere, the oxide, nitride or carbideof metal may also be formed by a reactive ion-plating process oractivated reactive evaporation process as the island-shaped portions 2.

Next, as shown in FIG. 4, on the major surface 1A of the base 1including the island-shaped portions 2 is formed a metal magnetic layer4 according to vacuum deposition, sputtering or the like means. As themetal magnetic layer 4, there can be utilized cobalt, cobalt-nickel orcobalt-nickel containing a small amount of iron or the like. The metalmagnetic layer 4 has a film thickness in a range from 700 Å to 2000 Å orabout 1500 Å according to the example of this invention and is formed bythe oblique evaporation.

As shown in FIG. 5, the outermost surface of the metal magnetic layer 4is subjected to the plasma treatment to form a layer 5 made of oxide,nitride, carbide, and so on. With the example of this invention, thesurface of the metal magnetic layer is treated by the plasma produced inthe aforesaid atmosphere a containing oxygen to form the oxide layer 5on the surface of the metal magnetic layer 4.

Thus, a desired magnetic recording medium 6 can be produced.

According to such magnetic recording medium, on one major surface 1A ofthe magnetic base 1, there is formed the discontinuous island-shapedportion 2 at least the surface of which is oxidized, nitrogenated orcarbonized through which the metal magnetic layer 4 is formed on thebase 1 so that the metal magnetic layer 4 can be strongly bonded to thebase 1. This may be considered that the adhesion of the oxide, thenitride or the carbide 3 which was formed by the plasma treatment of theisland-shaped portion 2 to the base 1 is strong so that the adhesion ofthe metal magnetic layer 4 formed thereon to the base 1 on theirboundary is improved. Forming continuously the layer 5 made of theoxide, nitride or carbide on the outermost surface of the metal magneticlayer 4 by plasma treatment enables an improved wear-proof property ofthe metal magnetic layer 4.

When the metal magnetic layer 4 is formed by the oblique evaporation, inorder that an incident angle θ at which a vapor-flow (flow of evaporatedparticle) is introduced into the base (in this case, the base is formedas a tape-shape) 1 may be made constant in each part of its evaporationrange, the evaporation may be made while moving the base 1 along apredetermined curve. The constant incident angle θ made so far enableshigh coercive force Hc and squareness ratio as were determined inadvance to be established and also efficiency of evaporation to beimproved.

We claim:
 1. A magnetic recording medium comprising a nonmagnetic base,a metal discontinuous layer formed on one major surface of saidnonmagnetic base as discrete island shapes and at least the surfaces ofwhich are oxidized, nitrogenated or carbonized, and a metal magneticlayer formed so as to cover completely said discontinuous layer and theportions of said nonmagnetic base which extend between said discreteisland shapes.
 2. A magnetic recording medium according to claim 1,wherein said discontinuous layer has a mean film thickness ranging from10 to 1000 Å.
 3. A magnetic recording medium according to claim 1,wherein the metal forming said discontinuous layer is cobalt.
 4. Amagnetic recording medium according to claim 3, wherein the surface ofsaid discontinuous layer is made of cobalt oxide.
 5. A magneticrecording medium according to claim 1, wherein said metal magnetic layeris made of cobalt or an alloy whose main component is cobalt.
 6. Amagnetic recording medium according to claim 1, wherein said metalmagnetic layer has on its surface formed a layer made of oxide, nitrideor carbide of metal constructing said metal magnetic layer.